CZ2005294A3 - Nanostructured working electrode of electrochemical sensor, process for its manufacture and sensor comprising such working electrode - Google Patents

Abstract

A nanostructured working electrode of an electrochemical sensor which is made of a film-like material and is inserted into the sensor. Thus, working electrodes can be formed from materials whose use in the known working electrodes has not been possible (eg from metals of defined purity). The invention further provides a method for producing a nanostructured working electrode and an electrochemical sensor comprising a nanostructured working electrode.

Description

A nanostructured working electrode of an electrochemical sensor, a method for its manufacture and a sensor comprising the working electrode

Technical field

The invention relates to nanostructured working electrodes of electrochemical sensors, to a process for their manufacture and to sensors comprising such working electrodes.

BACKGROUND OF THE INVENTION

The preparation of electrochemical sensors by screen printing is known (CZ 291411) and enables inexpensive and efficient production of electrochemical sensors and biosensors. The principle of preparation of working electrodes of such electrochemical sensors is to apply pastes containing active materials by screen printing. The active material (mostly gold, platinum, silver) is dispersed in the form of very fine grains in the carrier, which ensures that the material is in the form of a paste. This paste is applied by printing onto a suitable substrate. Thereafter, the paste is cured or fired to form the active sensor layer, or the carrier material is expelled and sintered to form the active electrode layer of the electrochemical sensor. The disadvantage of this procedure is not only the porosity and complexity of the surface structure of the printed layer, but also that the carrier material can significantly affect the detection capability of the electrode. The final functional properties of the working electrode are given by curing the binder or sintering the matured paste. In all cases, the grain relief is transferred to the resulting geometric shape of the working electrode surface. However, in some cases the surface quality plays a decisive role in the final application.

The above method of preparing the working electrode is advantageous in those applications where a large area of the working electrode of the sensor is needed. In many applications, however, the porosity and complexity of the surface structure of the printed layer is a disadvantage. This is particularly the case when the surface of the working electrode is modified with bioactive substances such as antibodies or DNA segments. For DNA segments, surface inhomogeneities directly affect <

the reproducibility of the hybridization process. Another disadvantage of working electrodes with a complex surface structure is that in some cases the immobilized biochemical layer can significantly block mass transfer between the environment, the bioactive sensor layer on the working electrode, and the actual working electrode of the sensor.

There are known ways to improve the working electrode structure. one of them is

EP 1300897, where a more homogeneous nanostructure is achieved by inserting a nanoporous ceramic element. Another option is to imprint a suitable matrix that will deliver the nanostructure to the working electrode. EP 1342736 describes this process and the materials that make it possible. The controlled sintering process of the nanoparticle electrodes is described in EP 1244168 and EP 1207572. Another possibility is to apply a suitable substance to the electrode surface to form the desired nanostructure by a further technological process (mentioned in US Patent No. 6,060,121). Another way of improving the properties of the working electrode is to use the nanostructured filler from which the working electrode is formed, as disclosed in Patent Application No. WO 98/56854. Other methods for transferring nanostructures to a working electrode are described in US 2004/241896 and WO 2004/052489. However, the abovementioned processes for improving the performance of the working electrodes also have disadvantages. In particular, it does not solve the problem of achieving a very homogeneous structure of the electrode surface. The methodologies are expensive and difficult to convert into mass production.

Another major problem with the existing process for screen printing electrodes is that the number of materials that can be processed by screen printing (i.e., grains in paste) is limited. For example, there are many materials that are so-called nanostructured - ie materials that have a periodic structure with a characteristic dimension of less than 1 µm on the surface. For example, pyramidal field electrodes with a base of 100 nm (CVD diamond anisotropic film and electrode for electrochemical sensing, KL Soh, WP Kang, JL Davidson, YM Wong, A. Wisitsor-at, G. Swain, DE Cliffel, Sensors are known and Actuators B 91, 2003, 39-45). Most of these materials can only be prepared as films or very small objects that cannot be incorporated into working electrode sensors using existing technologies. A number of other methods are known for preparing nanostructured materials in the form of films. Patent No. EP 1443091 describes chemical processes and compounds that enable the preparation of nanostructured films. Different methods for preparing nanostructured films are known from patents and applications US 2002/106447, WO 99/35312, WO 01/27690, US 6,301,038 and WO 2004/011672.

All of the above drawbacks of the prior art are overcome by the present invention.

SUMMARY OF THE INVENTION

The object of the present invention is a nanostructured working electrode of an electrochemical sensor, the principle of which is that the active surface of the electrode is formed by a material in the form of a foil having a thickness of 0.1-100 µm inserted at the working electrode of the sensor.

It is a further feature of the present invention that the film is prepared from a suitable material, for example, a pure metal or a suitable alloy, or even non-metal. The foil may be of an element selected from the group consisting of metals of the groups ΙΑ, IIA, IIIA, IVA, VA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB and IIB of the periodic table, metalloids and non-metals of ΠΙΑ and IVA of the periodic table and lanthanides .

Another feature of the invention is that the film may be an alloy of at least two metals selected from the group consisting of metals of Groups IA, IIA, IIIA, IVA, VA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB and IIB of the Periodic Table.

Another feature of the present invention is that the film can also be prepared from magnetic permeability alloys such as mumetal.

According to the invention, the working electrode film can also be prepared from high temperature superconductors.

Another feature of the invention is that other structures may be deposited or immobilized on the film. For example, metals or other structures may be deposited on a film of dielectric or semiconductive material (e.g., metal oxides) by, for example, the processes disclosed in patents and published applications US 2002/106447, WO 99/35312, WO 01/27690,

US 6,301,038 and WO 2004/011672, or a layer of organic molecules may be deposited on the film by the SAM (self-assembled monolayer) method.

It is an object of the present invention to provide a nanostructured working electrode of an electrochemical sensor according to the invention, comprising forming a sheet of 0.1-100 µm thick sheet material that is 11000 µm larger than a desired active surface area The carrier electrode is applied to the substrate in place of the working electrode. The carrier paste is then applied with a flame shape using a micromanipulator, then the working electrode is cured and subsequently a part of the working electrode surface is overprinted with dielectric paste and cured again.

Flat shapes can be prepared, for example, by punching with a punch.

The carrier paste applied to the working electrode site provides a conductive connection between the working electrode leads and the intermediate flame active electrode surface formed from the film. The paste has the property that it does not contain volatile substances which, when cured by leakage, would cause movement or changes in the shape of the inserted film. An example of such a paste is, for example, a conductive epoxy. A die cut flame shape is applied to the applied carrier paste by a micromanipulator, wherein the shape of the tool by which the flame shape is transmitted is adapted to prevent nanostructure damage or the working electrode structure is completed by the micromanipulator tool.

The carrier paste with an inserted flame electrode is cured at a temperature of 0-150 ° C. Production is completed by printing a dielectric layer that covers the conductive joints, edges of the working electrode, and delimits the final size of the working electrode area.

The attachment of the nanostructured film can be accomplished, for example, by reconciling the carrier paste containing the gold and / or platinum and / or silver particles at a temperature of 350-1000 ° C.

If the film used to prepare the working electrode is too thick, in the preferred embodiment of the invention, a recess is provided in the support that ensures that the working electrode is flush with the support and can be partially covered by the dielectric paste, thereby defining the final functional surface of the electrode.

The present invention further provides an electrochemical sensor comprising a working electrode according to the invention. The reference and auxiliary electrodes of the electrochemical sensor may be formed by any of the known methods, for example by screen printing (CZ 291411) or by pad printing.

The nanostructured working electrode sensors of the present invention are particularly useful for DNA detection. With the technology of the present invention, structures consisting of an array of electrodes of 10-100 nm can be formed. DNA is immobilized to individual field electrodes. Between the individual electrodes is a free space that facilitates hybridization. The invention makes it possible to improve the properties of DNA sensors.

Sensors with embedded nanostructured working electrode can also be used to determine heavy metals. Electrochemical determination of heavy metals by dissolving voltammetry on a mercury electrode is known. Mercury is toxic, but there is a possibility of bismuth replacement. Methods of determination are described in the literature where the electrode is formed by a paste consisting of a mixture of graphite and bismuth, but the results are very unrepeatable. By the method according to the invention, it is possible to form an electrode from a homogeneous layer of bismuth, which in the form of a foil is inserted in place of the working electrode of the sensor.

The use of bismuth (Bi) film is also an example of how the application of the invention improves the cleanliness of the electrode surface. In the classical preparation of a working electrode from a paste containing bismuth grains and graphite grains, organic substances from the binder paste and possibly other trace impurities contained in the material are adsorbed onto the bismuth surface. In fact, the history of bismuth in the paste is very difficult to trace. When forming a working electrode according to the invention, it is possible to use a foil of defined purity (eg 99.99%) and during the entire manufacturing process the active sensor surface only comes into contact with the teflon tool of the micro manipulators. working electrode purity (resulting in a sensor with a defined working electrode purity of 99.99%).

Embedded nanostructured working electrodes are also suitable for self-assembled monolayer (SAM) deposition of organic molecules. SAM-based biochemically active particle and biomolecule technology requires an extremely smooth and clean surface that cannot be achieved by printing the active material. An extremely smooth and clean surface can be achieved by inserting special foil materials, some of which have guaranteed surface inhomogeneity in atomic layer units (eg silicon foil), in place of the working electrode. SAM layers for attaching biomolecules to the flame electrode can be formed and nanostructured prior to insertion into the sensor. This sensor with nanostructured flame working electrode can be used for electrochemical determination of activity of immobilized biomolecules. As a result of nanostructure, the transfer of detected substances between the biomolecule and the electrode surface can be improved, thus increasing the signal and detection sensitivity.

The invention also allows the preparation of glassy carbon electrodes, which are a material for electrochemical assays with very wide application. Glass carbon cannot be prepared by printing. However, it is available in the form of microfoils. ((www.goodfellow.com)).

If active sensor layers are to be prepared from materials such as osmium, iridium, rhodium, glass metals and many others, it is virtually impossible, either for physicochemical or chemical reasons, to convert these materials into a paste and apply them by printing. All of these materials are available in the form of films, and can be used as materials for preparing the working electrodes of the present invention. The process according to the invention also enables the preparation of working electrodes from high-temperature superconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

The sensor consists of a working electrode (1) which is separated from the reference electrode (2) by a ring (6) of hydrophobic dielectric material and an auxiliary electrode (3) concentrically arranged around the reference electrode (2) and partially covered with hydrophobic dielectric material (7) . The working electrode consists of a printed layer (1c) defining the location of the working electrode, the carrier paste layer (1b) and the active surface (1a). The active surface of the working electrode is formed by a wheel cut from a sheet of active material. The conductive tracks (4) ending with the connecting pads (5) for connecting the working electrode, the reference electrode and the auxiliary electrode are printed by screen printing.

Giant. 1 is a top view of the described sensor.

Giant. 2 is a side view of the described sensor.

Giant. 3 is a side view of the described sensor, showing an embodiment of the invention wherein a recess is formed in the substrate.

Giant. 4 shows an electrode with a field of nanostructured electrodes formed on a silicon layer.

DETAILED DESCRIPTION OF THE INVENTION

The invention is illustrated in more detail by, but not limited to, the following examples.

He did

The conductive tracks of silver are printed on the corundum pad, the finished plate is left to stand at room temperature for 15 minutes, dried at 150 ± 20 ° C for 15 to 20 minutes and then baked at 850 ° C. In the next step, the working layer, i.e. the printed layer of the working electrode and the auxiliary electrode, which is left to lie, dry and burn under the same conditions, is screen-printed with AuPd. The reference electrode is printed from Ag / AgCl. After mating, the motif is cured at 150 ° C for 15 min. The die is punched from an Au foil on both sides covered with protective foils. Protective foils are removed from the die-cut wheel. Instead of the working electrode, a polymer paste is applied, which is the carrier medium for the die-cut wheel. The wheel is placed on the working electrode surface by a micromanipulator. Allow to stand for 15 minutes and dry at 150 ± 20 ° C for 15 to 20 minutes. The last layer is printed with a dielectric polymer paste. Printing this layer overlaps the edges of the die-cut wheel. Allow to rest and cure for 60 minutes at 150 ° C.

Example 2

The conductive tracks of silver are printed on the corundum pad, the finished plate is left to stand at room temperature for 15 minutes, dried at 150 ± 20 ° C for 15 to 20 minutes and then baked at 850 ° C. In the next step, the working layer, i.e. the printed layer of the working electrode and the auxiliary electrode, which is left to lie, dry and burn under the same conditions, is screen-printed with AuPd. The reference electrode is printed from Ag / AgCl. After mating, the motif is cured at 150 ° C for 15 min. The punch is a die cut from both sides of a covered bismuth (Bi) foil. Bi foil is supplied on mylar carrier foil, the other side is protected from damage when punched with protective foil. Instead of the working electrode, a polymer paste is applied, which is the carrier medium for the die-cut wheel. The protective foil is removed from the die-cut wheel. The wheel is placed on the working electrode surface by the Bi side with a micromanipulator. Mylar foil is removed. Allow to stand for 15 minutes and dry at 150 ± 20 ° C for 15 to 20 minutes. The last layer is printed with a dielectric polymer paste. Printing this layer overlaps the edges of the die-cut wheel. Allow to rest and cure for 60 minutes at 150 ° C.

Industrial applicability

The nanostructured working electrode sensor of the present invention can be widely used in the chemical and food industries, in ecology to monitor environmental pollution, and in medicine for inexpensive clinical analyzes.

Claims (11)

PATENT CLAIMS A nanostructured working electrode of an electrochemical sensor, characterized in that the active surface of the electrode is formed by a material in the form of a foil having a thickness of 0.1 - 100 μιη inserted at the working electrode of the sensor. The nanostructured working electrode of an electrochemical sensor according to claim 1, characterized in that the film is selected from the group consisting of metals of groups IA, IIA, IIIA, IVA, VA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, and IIB of the Periodic Table, lanthanides and semi-metals and non-metals of Groups IIIA and IVA of the Periodic Table. The nanostructured working electrode of an electrochemical sensor according to claim 1, characterized in that the film is of an alloy of at least two metals selected from the group consisting of metals of groups IA, IIA, IIIA, IVA, VA, IIIB, IVB, VB, VIB, VIIB, VIIIB , IB and IIB of the periodic table. The nanostructured working electrode of the electrochemical sensor of claim 1, wherein the foil is of a high-permeability magnetic alloy. The nanostructured working electrode of the electrochemical sensor of claim 1, wherein the film is a high temperature superconductor. Nanostructured working electrode of an electrochemical sensor according to any one of claims 1 to 5, characterized in that further structures are deposited or immobilized on the film. Method for producing a nanostructured working electrode of an electrochemical sensor according to any one of claims 1 to 6, characterized in that from a material in the form of a foil with a thickness of 0.1 - 100 μιη, flame shapes are prepared which are 1-1000 pm larger than the required shape of the active electrode surface, a carrier paste is applied to the substrate instead of the electrode, then a flame shape is applied to the micromanipulator, then the electrode is cured and then part of the electrode surface is overprinted with a dielectric paste and cured again. 8. A method for producing a nanostructured working electrode of an electrochemical sensor according to claim 7, wherein the carrier paste is free of volatile substances. The method of manufacturing a nanostructured working electrode of an electrochemical sensor according to claim 7, characterized in that the working electrode is bonded to the substrate during the first curing by sintering a paste containing gold and / or platinum and / or silver particles at a temperature of 350-1000 ° C. 10. The method of manufacturing a nanostructured working electrode of an electrochemical sensor according to claim 7, characterized in that a recess is formed in the substrate so that the surface of the working electrode formed by the thicker film is flush with the substrate. 11. An electrochemical sensor comprising a nanostructured working electrode according to any one of claims 1 to 6.